Fix launch GUI in IntelliJ with bad preferences and reduce logs

## Fix launch GUI in IntelliJ with bad preferences
### Context
This library has a client execution and release tests.
We use a main window to launch and test the segmentation gui. 
This window is implemented in a test class, so the gui execution in IntelliJ uses the test classpath.

### Description
As IntelliJ uses the production resources AND the test resources, the main window was loading a unit test preference file instead of the production one.
To fix this behaviour, we refactored the unit tests so that preferences are loaded from a ```String``` and no more from a ```File```

## Reduce logs
### Context
The logs were too verbose for a production/acceptance environment.

### Description
Logs are less verbose.